As a feature of CNNhealth.com, our team of expert doctors will answer readers' questions. Here's a question for Dr. Gupta.

From Adam Balkcom, Atlanta, Georgia

Dr. Gupta,

I am a personal trainer devoted to bringing my clients into optimum fitness and nutrition.

Something I have been hearing a lot lately is that microwaving kills a lot of the nutrients in the food. I now cook everything in a toaster oven. Is this overkill?

My clients and I appreciate you helping us clear up confusion over getting the most from the foods we eat.

Answer

Adam, Thank you for your question and for working to bring better nutrition and fitness to your clients.

The truth is that, no matter how food is cooked, whether it’s steamed, boiled, microwaved, or – in your case– cooked in your toaster oven, any type of cooking will destroy some nutrients in foods. The key, according to the U.S. Department of agriculture, is to prevent excessive losses of vitamins and minerals by using proper preparation and cooking techniques.

Microwave ovens cook food using oscillating electromagnetic waves, much like radio waves. The energy penetrates your food and excites the water and fat molecules, creating energy in the form of heat. The heat is fairly evenly distributed in the food cooking it quickly and evenly, as opposed to boiling, baking or steaming, which heat foods from the outside until they are cooked inside. Because microwave cooking is generally faster, fewer vitamins will be destroyed in the cooking process.

Water, heat, air, and light can be the enemies of nutrients in foods. They can also be diminished if food is cooked in water that’s too acidic or is too alkaline.

Foods can contain both fat-soluble vitamins, which include vitamins A, D, E, and K, and water-soluble vitamins, which include vitamin C and the B vitamins. Water-soluble vitamins are less stable and can be destroyed by water, heat, air and light.

The USDA advises that the key to avoid losing nutrients is by carefully handling and preparing foods.

*Water: Avoid soaking foods in water, which dissolves water soluble vitamins and minerals. Use as little water as possible when boiling, and incorporate the vitamin-rich water into other dishes such as soups and sauces. Steaming is preferable to boiling. Some foods, such as rice, pasta and beans, are coated with vitamins and minerals, so soaking or rinsing will diminish nutrients and should be avoided.

*Light: Allowing foods to stand in open light for prolonged periods can destroy some vitamins. Milk, for example, which is a good source of the B vitamin riboflavin, will lose much of that vitamin when left exposed to light. Light obstructing cardboard containers can help prevent this vitamin loss.

*Air: Exposure to air destroys vitamins A, C, E, K, and the B vitamins. To reduce vitamin loss cut and cook vegetables in big chunks so that less surface area is exposed to the air. Cook vegetables soon after cutting until just tender. Even better is to serve raw vegetables and fruits whenever possible.

*pH Balance: Do not add baking soda to vegetables when cooking because it makes the water alkaline and destroys thiamin and vitamin C.

The bottom line, Adam, is that your toaster oven may be overkill. Microwave cooking exposes most foods to less heat, water, and for shorter cooking periods, so that means that fewer vitamins will be destroyed during cooking. If time is a factor, microwaving is much quicker too

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sudhakar kaushik

Dr. Gupta: that is great to know microwave cooking is a superior option, other things remaining the same. If I may, could you please also advise and clear up confusion on the type of utensil and covering/not covering while cooking in a microwave. We now hear plastics for water is bad; plastics in microwave is bad and is there any truth to story about cooking foods without lids in a microwave may contaminate the food (radiation?)

There could be some concern about containers which are used to heat the food in microwave-usually plastic and the chance of some components leaking into the food, especially when foods high in fat are cooked in the microwave. However at this point it is really not clear whether this is the case or not as there is not to much research on the subject.

Hi, There are two established factors that affect the nutritive value of microwave-cooked foods. One is the plastic- as mentioned in other comments- Using unsafe plastic is a significant concern. The other- several studies have shown that some specific B-complex vitamins are lost in microwave cooking- it only applies to some vitamins, not all.. but for those, the difference is remarkable. As long as you don't put ALL your food in the microwave, though, I'm sure you'd get your daily needs fulfiled.

I was concerned about the case I heard about a woman receiving blood during surgery that was microwaved before it was put used in her blood transfusion. It seems the general concern about microwaves and food is that it changes the food's molecular structure and it doesn't seem that there is enough research looking into this...

then please explain away this experiment: if you plant two seeds in seperate pots expose them to the same soil and lighting conditions, the only difference being one plant receives plain water and the other receives tap water that has been microwaved for 1 min. and cooled down. The plant that received the microwave water is siginificantly smaller than the plant that received regular tap water....try it for yourself...

What are you attempting to test? If it's the effect of microwave exposure to water used for watering plants you're trying to test, you're using the wrong control; compare instead to water that has been boiled for the same amount of time on the stove (killing bacteria in the water; perhaps some of them were helpful).

I remember that "test" that some girl did as a school project claiming that microwaved water killed one plant while the other grew normally.. The story circulated the internet several times in the last year or so. If you read the whole story, however, she admitted to microwaving the water in a cheap plastic container, which would have leached something into the water (see previous comments about plastic in the microwave) and was more likely the cause of the plant's demise than the effects of the microwave itself.

Marnie, this experiment is all over the web and you're right, there could have been leaching from a plastic cup. However there may be other factors. I went to one of the many sites to see the photos.
1) There was only one plant each, this is a very small sample;
2) leaves had been cut off the MW water plant, the explanation being that they were dead, but who made that decision? Could there have been other factors?
3) The soil in the 2 pots is a different colour, the MW water pot is darker. Was it different soils? Was the MW watered plant wetter – possible waterlogging? Could it mean less water had evaporated because of less light or heat? A combination (waterlogged dark cold environment vs moist sunny and warm)?
4) Were the plants treated in the same way, watered with the same amounts at the same time?
5) There are no quantitative results, only a "just look at the pictures" of a full plant and one that's had its leaves cut off;
6) So many sites state "my granddaughter" one begins to wonder if this is a genuine school girl experiment or an adult with an opinion to prove.

My son also did this experiment for a high school science fair. 10 plants (raddishes) each for tap water, stove boiled in a pyrex container, microwave boiled in a pyrex container. All 30 plants kept on the same tray, same light, temperature and wind conditions, all fed at the same time with the same measured amounts of water. After 6 weeks the leaves were counted and length measured and any raddishes weighed. Plain tap water was measurably better. There was no significant difference between stove and MW boiled water – if anything there were more leaves and bigger raddishes in MW water.

The experiment was repeated by another boy the following year and a neighbour's son copied it at another high school but using different plants. Same results.

"Leukocytosis (an increase in white blood cells)," Hertel explained, "which cannot be accounted for by normal daily deviations such as following the intake of food, is taken seriously by haematologists. Leukocyte response is especially sensitive to stress. They are often signs of pathogenic effects on the living system, such as poisoning and cell damage. The increase of leukocytes with the microwaved foods was more pronounced than with all the other variants.

It appears that these marked increases were caused entirely by ingesting the microwaved substances." The cholesterol markers were very interesting, Hertel stressed: "Common scientific belief states that cholesterol values usually alter slowly over longer periods of time. In this study, the markers increased rapidly after the consumption of the microwaved vegetables. However, with milk, the cholesterol values remained the same and even decreased with the raw milk significantly."

Hertel believes his study tends to confirm newer scientific data that suggest cholesterol may rapidly increase in the blood secondary to acute stress. "Also," he added, "blood cholesterol levels are less influenced by cholesterol content of food than by stress factors. Such stress-causing factors can apparently consist of foods which contain virtually no cholesterol-the microwaved vegetables."

It is plain to see that this individually financed and conducted study has enough meat in it to make anyone with a modicum of common sense sit up and take notice. Food from the microwave oven caused abnormal changes, representing stress, to occur in the blood of all the test individuals. Biological individuality, a key variable that makes a mockery of many allegedly scientific studies, was well accounted for by the established baselines. So, how has the brilliant world of modern technology, medicine and 'protect the public' government reacted to this impressive effort?

A GAG ORDER

As soon as Hertel and Blanc announced their results, the hammer of authority slammed down on them. A powerful trade organization, the Swiss Association of Dealers for Electroapparatuses for Households and Industry, known simply as FEA, struck swiftly. They forced the President of the Court of Seftigen, Kanton Bern, to issue a 'gag order' against Hertel and Blanc.

The attack was so ferocious that Blanc quickly recanted his support-but it was too late. He had already put into writing his views on the validity of the studies where he concurred with the opinion that microwaved food caused the blood abnormalities. Hertel stood his ground, and today is steadfastly demanding his rights to a trial. Preliminary hearings on the matter have been appealed to higher courts, and it's quite obvious the powers that be do not want a 'show trial' to erupt on this issue. In March 1993, the court handed down this decision based upon the complaint of the FEA:"Consideration.

1. Request from the plaintiff (FEA) to prohibit the defendant (Dr Ing. Hans Hertel) from declaring that food prepared in the microwave oven shall be dangerous to health and lead to changes in the blood of consumers, giving reference to pathologic troubles as also indicative for the beginning of a cancerous process. The defendant shall be prohibited from repeating such a statement in publications and in public talks by punishment laid down in the law.

2. The jurisdiction of the judge is given according to law.

3. The active legitimacy of the plaintiff is given according to the law.

4. The passive legitimacy of the defendant is given by the fact that he is the author of the polemic [published study] in question, especially since the present new and revised law allows to exclude the necessity of a competitive situation, therefore delinquents may also be persons who are not co-competitors, but may damage the competing position of others by mere declarations.[Apparently, Swiss corporations have lobbied in a law that nails "delinquents" who disparage products and might do damage to commerce by such remarks. So far, the US Constitution still preserves freedom of the press.]

5. Considering the relevant situation it is referred to three publications: the public renunciation [sic] of the so-called co-author Professor Bernard Blanc, the expertise of Professor Teuber [expert witness from the FEA] about the above-mentioned publication, the opinion of the public health authorities with regard to the present stage of research with microwave ovens as well as to repeated statements from the side of the defendant about the danger of such ovens.

6. It is not considered of importance whether or not the polemic of the defendant meets the approval of the public, because all that is necessary is that a possibility exists that such a statement could find approval with people not being experts themselves. Also, advertising involving fear is not allowed and is always disqualified by the law. The necessity for a fast interference is in no case more advised than in the processes of competition. Basically, the defendant has the right to defend himself against such accusations. This right, however, in cases of pressing danger with regard to impairing the rights of the plaintiff when this is requested.

I dont think so..
I am using microwave since so many years..and i have never thought regarding this matter.
Thanks friend for creating this thought in mind which is necessary.
We peoples are using microwave to minimize our time but we are always thinking the positive factor but we should know the disadvantage of this so that we will conscious

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